THERMODYNAMICS OF OXYGEN SOLUTIONS IN BORON-CONTAINING Fe – Ni MELTS

Abstract

Fe – Ni alloys are widely used in modern technology. Boron is one of the alloying components in these alloys. Oxygen is one of the harmful impurities in Fe – Ni alloys, it presents in the metal in dissolved form or in the form of oxide nonmetallic inclusions. The presence of oxygen in these alloys degrades their service properties. The study of thermodynamics of the oxygen solution in boron-containing Fe – Ni melts is of considerable interest for the practice of such alloys production. Thermodynamic analysis of oxygen solutions in boroncontaining Fe – Ni melts has been carried out. The equilibrium constant of interaction of boron and oxygen dissolved in the Fe – Ni melts, the activity coefficients at infinite dilution, and the interaction parameters characterizing these solutions were determined for melts of different composition. In the interaction of boron with oxygen in Fe – Ni melts, the oxide phase, in addition to B2 O3 , contains FeO and NiO. Values of the mole fractions of B2 O3 , FeO and NiO in the oxide phase for different boron concentrations in Fe – Ni melts were calculated at 1873 K. In the case of an iron melt at low boron contents, the mole fraction of boron oxide is ~0.1. As the content of nickel and boron increases in the melts, the mole fraction of boron oxide in the oxide phase increases and, in the case of pure nickel, is close to unity. Dependences of the oxygen solubility on the contents of nickel and boron in the studied melts were calculated. With increasing nickel content in melt deoxidation ability of chromium increases significantly. The oxygen solubility curves in boron-containing Fe – Ni melts pass through a minimum whose position shifts to the higher boron content with an increase in the nickel content in melt. Boron contents in minimum points on the oxygen solubility curves and the corresponding minimum oxygen concentrations were determined.